The present invention relates to an optical densitometer for determining the density of radiosensitive films and in particular to a densitometer providing improved resolution and accuracy.
Radiosensitive films are used for radiation dose measurement, for example, in medical radiotherapy in which ionizing radiation is used to treat malignant cells in cancer or the like. Such films, which provide high spatial resolution, are particularly useful in advanced radiation therapy systems, such as intensity modulated radiation therapy (IMRT) in which complex, fine beam patterns must be measured. Generally, the films are sensitive to ionizing radiation and can provide a spatial resolution as little as 25 micrometers and a wide dynamic range from a few milliGray to greater than 40 Gray.
Radiochromic films are radiosensitive films that change color on exposure to ionizing radiation without the need for chemical or other processing. While such films can be used for qualitative dose measurement, normally they are scanned, for example, with a flatbed optical scanning mechanism and the measured film density, that is light absorption caused by the exposed film pigment, is applied to a calibration curve to yield a quantitative measurement of received radiation dose. The resulting scans may be further processed, for example, to extract isodose curves or other quantitative information.
While radiosensitive films provide advantages over ionization detectors and solid-state detectors in terms of spatial resolution and dynamic range, obtaining consistent quantitative results with radiosensitive films can be difficult.